Piezoelectric electronic component, and production method therefor, and communication equipment

ABSTRACT

A piezoelectric electronic component for use in a cellular phone or the like and capable of achieving reductions in size and profile is provided. A piezoelectric element oscillating in response to application of an input signal and outputting an output signal corresponding to the oscillations is provided on a substrate. The piezoelectric element includes a pad, the pad inputting and outputting the input and output signals. A shell member serving as a sealing member and having an insulation film covering the piezoelectric element is provided on the substrate, the shell member being remote from the piezoelectric element. The shell member includes a through hole above the pad, and the through hole is occluded with an electrode.

TECHNICAL FIELD

The present invention relates to a piezoelectric component that canachieve reductions in size and profile and that is suitable as a filterused in a small communication device, a process for producing thepiezoelectric component, and a communication apparatus.

BACKGROUND ART

In recent years, many types of filter have been used in smallcommunication devices, such as cellular telephones. Great demands forreductions in the size, profile, and weight of small communicationdevices also require reductions in the size, profile, and weight of suchfilters. Furthermore, in the small communication devices, an increase inthe amount of information required to be communicated, for example, theincrease of communication of images, has led to the communicationfrequencies being increased to GHz frequencies or higher.

Therefore, with such trends toward higher communication frequencies,piezoelectric filters and surface acoustic wave filters have become usedas the above-described filters.

Each of the piezoelectric filters includes a plurality of piezoelectricresonators connected so as to form a ladder network or a latticenetwork. The piezoelectric resonators each include, for example, a Sisubstrate having an opening or a depression and an exciter provided onthe Si substrate, the exciter covering the opening or the depression,and the exciter having a structure in which the upper and lower surfacesof a thin film portion having at least one piezoelectric thin film(composed of ZnO or AlN) are sandwiched between at least one pair of anupper electrode and a lower electrode, the upper electrode beingdisposed opposite the lower electrode. In such a piezoelectric filter,longitudinal oscillations generated along the thickness direction of theexciter are used; hence, it is necessary to ensure a space for theoscillations above the exciter and to protect the exciter from exposureto water, dust, and the like.

Each of the surface acoustic wave filters includes an interdigitalelectrode provided on a piezoelectric substrate composed of, forexample, quartz, LiTaO₃, or LiNbO₃. In such a surface acoustic wavefilter, it is necessary to ensure a space for oscillations above apropagation portion for surface acoustic waves on the interdigitalelectrode and the piezoelectric substrate and to protect theinterdigital electrode from exposure to water, dust and the like.

As disclosed in Japanese Unexamined Patent Application Publication No.5-275965 and shown in FIG. 14, in a known piezoelectric electroniccomponent including a piezoelectric filter or a surface acoustic wavefilter, a die bonding agent 75 is applied to the bottom surface of abox-shaped package 73 composed of alumina or the like, and apiezoelectric element 71, such as a piezoelectric filter or a surfaceacoustic wave filter, is mounted in the package 73 by die bonding. Afterbonding terminals in the package 73 to the corresponding electrodes ofthe piezoelectric element 71 with bonding wire 77, the opening of thepackage 73 is sealed with a lid 79 using solder 79 a.

As disclosed in Japanese Unexamined Patent Application Publication Nos.2002-232253 and 2000-49565, to enable a reduction in size, electrodelands are formed on the inner bottom surface of a package composed ofalumina or the like, a piezoelectric element, such as a piezoelectricfilter or a surface acoustic wave filter, is mounted on the electrodelands by flip-chip bonding. Then, the package is sealed with a lid.

However, in such a known structure, if a piezoelectric element, such asa piezoelectric filter or a surface acoustic wave filter, is reduced insize and profile, unless the package is also reduced in size andprofile, the total size of a piezoelectric electronic componentincluding the piezoelectric filter or a surface acoustic wave filtercannot be reduced, which is disadvantageous. Furthermore, in such aknown structure, the package is often composed of a poorly processablematerial, such as alumina; hence, a reduction in the size of the packagedisadvantageously increase the process cost of the package.

In particular, in the piezoelectric filter, the exciter is provided atthe opening or the depression of the substrate. Thus, impacts on theexciter in processing steps, such as dicing a piezoelectric element,picking up the piezoelectric element in mounting, and die bonding, cancause the destruction of the exciter, thereby disadvantageously reducingthe yield of the resulting piezoelectric electronic components,prolonging time required for dicing, and increasing cost.

DISCLOSURE OF INVENTION

To overcome the problems, a piezoelectric electronic component includesa substrate; a piezoelectric element provided on the substrate, thepiezoelectric element oscillating in response to application of an inputsignal, and the piezoelectric element outputting an output signalcorresponding to the oscillations; a plurality of pads provided at thepiezoelectric element; and a sealing member composed of an insulatingfilm, the sealing member covering the piezoelectric element and beingremote from the piezoelectric element, wherein the sealing memberincludes a through hole on each of the pads, the through hole connectingan internal space with an external space, the internal space beingensured by providing the sealing member so that the sealing member isremote from the piezoelectric element, and an electrode is provided soas to occlude the through hole.

In the above structure, by providing the sealing member so that thesealing member is remote from the piezoelectric element in thestructure, it is possible to protect the piezoelectric element withoutinhibiting the oscillations of the piezoelectric element, to provide thesealing member close to the piezoelectric element, and to achievereductions in size and profile. Furthermore, if an external force, suchas an impact, acts on the piezoelectric element, the external force ispartially absorbed into the sealing member, thereby improving impactresistance.

The sealing member is preferably composed of at least one compoundselected from the group consisting of a silicon nitride such as SiN, asilicon oxide such as SiO₂, an aluminum oxide such as Al₂O₃, an aluminumnitride such as AlN, a zinc oxide such as ZnO, a silicon oxynitride suchas SiO_(x)N_(y), and a tantalum nitride such as TaN.

Another piezoelectric electronic component of the present inventionincludes a substrate; a piezoelectric element provided on the substrate,the piezoelectric element oscillating in response to application of aninput signal, and the piezoelectric element outputting an output signalcorresponding to the oscillations; a plurality of pads provided at thepiezoelectric element; and a sealing member composed of an insulatingfilm, the sealing member covering the piezoelectric element and beingremote from the piezoelectric element, wherein the sealing member iscomposed of at least one compound selected from the group consisting ofa silicon nitride such as SiN, a silicon oxide such as SiO₂, an aluminumoxide such as Al₂O₃, an aluminum nitride such as AlN, a zinc oxide suchas ZnO, a silicon oxynitride such as SiO_(x)N_(y), and a tantalumnitride such as TaN.

In the structure, the sealing member is composed of at least onecompound selected from the group consisting of a silicon nitride such asSiN, a silicon oxide such as SiO₂, an aluminum oxide such as Al₂O₃, analuminum nitride such as AlN, a zinc oxide such as ZnO, a siliconoxynitride such as SiO_(x)N_(y), and a tantalum nitride such as TaN.Therefore, it is possible to protect the piezoelectric element withoutinhibiting the oscillations of the piezoelectric element, to provide thesealing member close to the piezoelectric element, and to achievereductions in size and profile. Furthermore, if an external force, suchas an impact, acts on the piezoelectric element, the external force ispartially absorbed into the sealing member, thereby improving impactresistance.

In the piezoelectric electronic component, the sealing member preferablyhas a multilayer structure and preferably includes at least one filmhaving a compressive stress and at least one film having a tensilestress.

In the piezoelectric electronic component, the film having a compressivestress may be composed of at least one compound selected from the groupconsisting of SiO₂, ZnO, and TaN. In the piezoelectric electroniccomponent, the film having a tensile stress may be composed of at leastone compound selected from the group consisting of Al₂O₃, SiN, and AlN.

In the piezoelectric electronic component, the sealing member has amultilayer structure, and the uppermost layer may be composed of aresin. In the piezoelectric electronic component, the resin may becomposed of at least one compound selected from the group consisting ofa polyimide, an epoxy resin, a resist resin, and a liquid-crystallinepolymer.

The piezoelectric electronic component may include a connecting holeprovided at the periphery of the sealing member, the connecting holeconnecting the interior of the sealing member with the exterior, and anelectrode provided so as to occlude the connecting hole, the electrodeinputting and outputting the input and output signals.

In the piezoelectric electronic component, the piezoelectric element maybe a piezoelectric resonator including a substrate having an opening ora depression and an exciter covering the opening or the depression, theexciter having a structure in which the upper and lower surfaces of athin film portion including at least one piezoelectric thin film aresandwiched between at least one pair of an upper electrode and a lowerelectrode, the upper electrode and lower electrode being disposedopposite each other.

In the piezoelectric electronic component, the piezoelectric element maybe a piezoelectric filter including a plurality of piezoelectricresonators, each containing a substrate having an opening or adepression and an exciter covering the opening or the depression, theexciter having a structure in which the upper and lower surfaces of athin film portion including at least one piezoelectric thin film aresandwiched between at least one pair of an upper electrode and a lowerelectrode, the upper electrode and lower electrode being disposedopposite each other.

In the piezoelectric electronic component, the piezoelectric element maybe a surface acoustic wave device having at least one interdigitalelectrode on a piezoelectric substrate. In the piezoelectric electroniccomponent, an electrical circuit may be provided on the sealing member.

To overcome the problems, in a process for producing a piezoelectricelectronic component in order that a sealing member composed of aninsulating film includes a cavity to cover a piezoelectric element on asubstrate, the sealing member being remote from the piezoelectricelement, the process includes the steps of: forming a sacrificial layeron the piezoelectric element, the sacrificial layer corresponding to thecavity; forming the sealing member on the entire surface of thesacrificial layer; partially removing the sealing member to form anexposed portion partially exposing the sacrificial layer; and removingthe sacrificial layer from the exposed portion.

In the process, the sealing member is partially removed to form anexposed portion partially exposing the sacrificial layer. Therefore, itis possible to ensure the removal of the sacrificial layer from theexposed portion and to ensure the formation of the sealing membercomposed of the insulating film and including the cavity, the sealingmember being remote from the piezoelectric element.

Furthermore, in the process, when the sacrificial layer having a smallthickness is provided, the sealing member on the sacrificial layer canbe disposed close to the piezoelectric element and can be integrallyprovided with the substrate. Thereby, it is possible to achievereductions in the size and profile of the resulting piezoelectricelectronic component.

In the production process, the sacrificial layer may be formed into ataper, the height of the taper decreasing toward one of the ends of theformed pattern of the sacrificial layer. According to the process, thesacrificial layer is formed into a taper, the height of the taperdecreasing toward one of the ends of the formed pattern of thesacrificial layer. Therefore, the height of the exposed portion servingas a drain for removing the sacrificial layer can be easily controlled,thus ensuring the formation of the cavity. In the production process,the exposed portion may be formed at a position facing a pad in thepiezoelectric element, the pad being used for inputting and outputtingsignals. According to the process, the exposed portion may be formed ata position facing a pad in the piezoelectric element, the pad being usedfor inputting and outputting signals. Therefore, the pad connecting tothe exterior can double as part of the drain for removing thesacrificial layer, thus simplifying the production process.

In the production process, the sacrificial layer may be formed on thepiezoelectric element and the substrate while part of a pad forinputting and outputting signals remains. According to the process, thesacrificial layer may be formed on the piezoelectric element and thesubstrate while part of a pad for inputting and outputting signalsremains. Therefore, it is possible to fix the piezoelectric element onthe substrate, the piezoelectric element being disposed between thesealing member and the substrate. Consequently, the impact strength ofthe resulting piezoelectric electronic component can be improved asdescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a piezoelectric electronic componentaccording to a first embodiment of the present invention.

FIGS. 2 (a) to (j) are each a process drawing showing a production stepof the piezoelectric electronic component.

FIGS. 3 (a) to (l) are each a process drawing showing another productionstep of the piezoelectric electronic component.

FIGS. 4 (a) to (f) are each a process drawing showing a production stepof a piezoelectric electronic component according to a second embodimentof the present invention.

FIG. 5 is a schematic circuit diagram of an example of a piezoelectricfilter.

FIG. 6 is a cross-sectional view of a piezoelectric electronic componentaccording to a third embodiment of the present invention.

FIG. 7 (a) is a plan view of the piezoelectric electronic component, (b)is a cross-sectional view of the piezoelectric electronic componenttaken along line X-X′ in (a), and (c) is a plan view showing anelectrode structure by virtually removing the shell member from thepiezoelectric electronic component.

FIG. 8 shows an example of a sacrificial layer used for producing apiezoelectric electronic component of the present invention, (a) is aplan view, and (b) is a perspective view.

FIG. 9 is a cross-sectional view of another example of a piezoelectricfilter using the piezoelectric electronic component.

FIG. 10 shows a piezoelectric electronic component according to a fourthembodiment of the present invention, (a) is a plan view, (b) is across-sectional view taken along line X-X′ in (a), and (c) is a planview showing a conductor for forming an inductor on the shell member ofthe piezoelectric electronic component.

FIG. 11 is a plan view of a piezoelectric element used in apiezoelectric electronic component according to a fifth embodiment ofthe present invention.

FIG. 12 shown the piezoelectric electronic component according to thefifth embodiment, (a) is a cross sectional view, and (b) is a plan view.

FIG. 13 shows a modified example of the piezoelectric electroniccomponent according to the fifth embodiment, (a) is a cross-sectionalview, and (b) is a plan view.

FIG. 14 is an exploded cross-sectional view of a known piezoelectricelectronic component.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described on the basisof FIGS. 1 to 13.

First Embodiment

A piezoelectric component according to a first embodiment of the presentinvention will be described on the basis of FIGS. 1 to 3.

As shown in FIG. 1, the piezoelectric component includes a piezoelectricelement 3 for producing oscillations according to an applied inputsignal and outputting an output signal corresponding to theoscillations, a shell member (sealing member) 5 covering thepiezoelectric element 3 and being remote from the piezoelectric element3, through holes 5 a provided at the periphery of the shell member 5,the through holes 5 a each connecting the internal space provided withthe shell member 5 and the exterior, and a plurality of electrodes 17for inputting and outputting the input signal and the output signal,respectively, the electrodes 17 filling in the through holes 5 a. Thethrough holes 5 a are filled with the electrodes 17 to securehermeticity of the internal space and to permit the input and output ofthe electrical signals between the piezoelectric element 3 and theexterior.

The shell member 5 covering piezoelectric element 3 and being remotefrom the piezoelectric element 3 includes a cavity 5 c serving as aninternal space and a plurality of connecting holes 5 b. The connectingholes 5 b are disposed at the periphery of the cavity 5 c, and serve aspaths for introducing an etchant for forming the cavity 5 c and thendraining etched component dissolved in the etchant to the exterior.

A material constituting the shell member 5 preferably has the followingproperties: (1) being insulating; (2) ensuring hermeticity; and (3)having resistance to an etchant for a sacrificial layer 9 describedbelow.

The piezoelectric element 3 is an piezoelectric resonator including asilicon (Si) substrate 1 having an opening 1 a and an exciter(diaphragm) 3 d provided above the opening 1 a, the exciter 3 d having astructure in which the upper surface and the lower surface of a thinfilm portion including at least one piezoelectric thin film 3 b aresandwiched between at least one pair of an upper electrode 3 c and alower electrode 3 a, the upper electrode 3 c and lower electrode 3 abeing disposed opposite each other. In the piezoelectric element 3, adepression having a space between the exciter 3 d and the siliconsubstrate 1 may be provided in place of the opening 1 a provided throughthe silicon substrate 1 in the thickness direction. An insulating film 2is provided on the entire surface of the silicon substrate 1, theinsulating film 2 being disposed between the silicon substrate 1 and theexciter 3 d. Examples of the insulating film 2 include single-layerinsulating films composed of silicon nitrides such as SiN, siliconoxides such as SiO₂, aluminum oxides such as Al₂O₃, aluminum nitridessuch as AlN, zinc oxides such as ZnO, silicon oxynitrides such asSiO_(x)N_(y), or tantalum nitrides such as TaN; and insulating filmseach having a multilayer structure in which two or more layers of asingle-layer insulating film are stacked.

The upper electrode 3 c further includes a strip-shaped first leadextending from the exciter 3 d to one end (first direction) of thesilicon substrate 1 along the surface of the silicon substrate 1; and asubstantially rectangular flat first pad 3 c ₁ at the end of the firstlead. The lower electrode 3 a further includes a strip-shaped secondlead extending from the exciter to the other end (second directionopposite the first direction) of the silicon substrate 1 along thesurface of the silicon substrate 1; and a substantially rectangular flatsecond pad 3 a ₁.

The plurality of electrodes 17 are electrically connected to the firstpad 3 c ₁ and the second pad 3 a ₁ at the bottom of each of theelectrodes 17, and occlude the connecting holes 5 b and the throughholes 5 a. Furthermore, the electrodes 17 each include a flange 17 a atthe end of the electrodes 17, the flange 17 a extending outwardly on thesurface of the shell member 5 along the surface of the shell member 5.

The shell member 5 is also fixed on the silicon substrate 1 with theflanges 17 a. Therefore, even if external forces, such as vibrations andimpacts, are applied to the silicon substrate 1, the external forces actseparately on the piezoelectric element 3 and the shell member 5, thussuppressing the power of the external forces applied to thepiezoelectric element 3. Thereby, it is possible to protect thepiezoelectric element 3.

The shell member 5 is fixed on the silicon substrate 1 at the peripheryof the shell member 5. Furthermore, part of the periphery of the shellmember 5 is disposed on the silicon substrate 1 with at most threeperipheral edges of the first pad 3 c ₁ therebetween, except for the endof the first pad 3 c ₁ connected to the first lead. Another part of theperiphery of the shell member 5 is disposed on the silicon substrate 1with at most three peripheral edges of the second pad 3 a ₁therebetween, except for the end of the second pad 3 a ₁ connected tothe second lead.

In this way, the periphery of the shell member 5 is fixed on the siliconsubstrate 1 with part of the first pad 3 c ₁ and part of the second pad3 a ₁ therebetween. Therefore, even if external forces, such asvibrations and impacts, are applied to the silicon substrate 1, theexternal forces act separately on the piezoelectric element 3 and theshell member 5, thus suppressing the power of the external forcesapplied to the piezoelectric element 3. Thereby, it is possible toprotect the piezoelectric element 3.

Next, steps included in a process for producing the piezoelectriccomponent will be described below with reference to FIGS. 2 (a) to (j)and FIGS. 3 (a) to (l).

In the production process, as shown in FIGS. 3 (a) and (b), theinsulating film 2 is entirely formed on a surface of the siliconsubstrate 1 having a substantially rectangular parallelepiped shape.Then, the piezoelectric element 3 having the structure of a bulkacoustic wave (BAW) resonator including lower electrode 3a/piezoelectric thin film 3 b/upper electrode 3 c is formed on theinsulating film 2. Subsequently, the silicon substrate 1 is subjected toanisotropic etching from the side opposite the surface having thepiezoelectric element 3 toward the piezoelectric element 3, therebyforming the opening 1 a.

At this time, the anisotropic etching is performed in a manner such thata portion of the silicon substrate 1 having a thickness of several tensof micrometers is formed at a position facing the piezoelectric element3 to form a thin film-supporting portion 1 b for supporting the exciter3 d on the silicon substrate 1.

Subsequently, as shown in FIGS. 3 (c) and (d) and FIG. 2 (a), thepattern of the sacrificial layer 9 is formed on the piezoelectricelement 3 by photolithography. When the pattern of the sacrificial layer9 is formed, proximity exposure, in which exposure is performed while amask is remote from an object to be etched, is performed. Thereby, ataper 9 a whose height gradually decreases toward the outside (edge ofthe pattern) is formed at the periphery of the sacrificial layer 9.

By providing such a taper 9 a, the size of the connecting hole 5 b canbe controlled. Furthermore, as described below, the formation of thecavity 5 c, which is the internal space of the shell member 5, can bestabilized, and the entry of an electrode material into the cavity 5 ccan be suppressed in forming an electrode 7. Thereby, it is possible tostabilize the production of the piezoelectric component.

The sacrificial layer 9 should be composed of a material such that anetchant for removing the sacrificial layer 9 by dissolution does notcause damage to the thin film material of the piezoelectric element 3and the shell (exterior) member. Examples of the material of thesacrificial layer 9 include water-soluble antimony (Sb), resins (e.g.,resist resins) removable with an organic solvent, zinc oxide (ZnO) andgermanium (Ge) capable of being etched with a dilute acid, andphosphosilicate glass (PSG) and polysilicon capable of being dissolvedin hydrofluoric acid. Zinc oxide has satisfactory heat resistance andthus can be used to form the shell member. A SiN film or a SiO₂ filmhaving satisfactory film quality and requiring a high film-formingtemperature can be used.

When the sacrificial layer 9 is formed on the piezoelectric element 3,the sacrificial layer 9 does not cover the entire surface of thepiezoelectric element 3. That is, the sacrificial layer 9 is formed in amanner such that the sacrificial layer 9 covers the area of thepiezoelectric element 3 other than the periphery of the pad 3 a ₁, whichis used for electrically connecting to the exterior, of the lowerelectrode 3 a and the periphery of the pad 3 c ₁, which is used forelectrically connecting to the exterior, of the upper electrode 3 c ofthe piezoelectric element 3. Consequently, the shell member 5 will beformed on the silicon substrate 1 with the peripheries of the pads 3 a ₁and 3 c ₁ of the respective lower and upper electrodes 3 a and 3 cprovided therebetween; hence, the strength of the piezoelectric element3 bonded to the silicon substrate 1 can be improved.

As shown in FIGS. 2 (b) and FIGS. 3 (e), the film of the shell member 5is formed on the entire surface of the sacrificial layer 9 and thesilicon substrate 1. The shell member 5 is preferably composed of amaterial having a low membrane stress and satisfactory hermeticity andmoisture resistance. An example of thereof is a silicon dioxide (SiO₂)film formed by RF sputtering.

Subsequently, as shown in FIG. 2 (c), a resist film 15 is formed on theshell member 5, and windows 15 a for etching are formed at positionscorresponding to the pads by photolithography. As shown in FIG. 2 (d),the corresponding portions of the shell member 5 are removed by etchingthrough the windows 15 a.

As shown in FIGS. 3 (f) and (g) and FIG. 2 (e), the remaining resistfilm 15 is removed. At this time, the through holes 5 a for exposing thetapers 9 a, which are disposed at the periphery of the sacrificial layer9, at the pads 3 a ₁ and 3 c ₁ are formed in the shell member 5.

Subsequently, as shown in FIG. 2 (f) and FIGS. 3 (h) and (i), thesacrificial layer 9 is removed with a solvent capable of dissolving thesacrificial layer 9 (for example, when the sacrificial layer 9 iscomposed of a resist resin, the solvent is acetone or the like) via thethrough holes 5 a and the exposed tapers 9 a to form the cavity 5 c thatis an internal space in the shell member 5, the cavity 5 c beingdisposed between the exciter 3 d of the piezoelectric element 3 and theinner surface of the shell member 5. At this time, connecting holes 5 bhaving tapered shapes corresponding to the respective tapers 9 a areformed in the periphery of the shell member 5.

Next, the thin film-supporting portion 1 b remaining at a positionadjacent to the back surface of the exciter 3 d is removed. As shown inFIG. 2 (g), the electrode layer 17 composed of copper or the like isformed on the shell member 5 and formed in a manner such that thethrough holes 5 a and the connecting holes 5 b are filled with theelectrode 17.

The electrode 17 is preferably formed by a film-forming methodexhibiting a satisfactory coverage, for example, CVD or sputtering.Sputtering is more preferable. In the film formation, the cavity 5 c issealed with the electrode 17 under a pressure during the film formation.Alternatively, the film formation may be performed by applying a metalpaste onto a predetermined position by mask printing and then heating.

Subsequently, as shown in FIG. 2 (h), the unnecessary region of theelectrode layer 17 is removed using a resist layers 19 for patterningthe electrode, each of the resist layer 19 covering the correspondingthrough hole 5 a and covering a region extending from the peripherytoward the outside. Next, the remaining resist layers 19 are removed toform the electrodes 17 shown in FIG. 1, as shown in FIG. 2 (i) and FIGS.3 (j) and (k).

According to need, as shown in FIG. 2 (j), solder portions 7 may beformed on the electrodes 17 by printing. Alternatively, if theconnecting holes 5 b are sealed, solder balls may be formed. In the caseof using solder, when the shell member 5 is composed of a material thatlack an affinity for solder, for example, SiO₂, metal layers composed ofa metal (for example, nickel) having an affinity for solder arepreferably formed at regions of the shell member 5, each of the regionsurrounding the opening of each through hole 5 a. Furthermore, as shownin FIG. 3 (i), a back plate 19 for occluding the opening 1 a may bemounted.

A resin layer composed of a polyimide or the like and functioning as areinforcing component may be formed on the outermost layer of the shellmember 5. In such piezoelectric electronic components, a plurality ofpiezoelectric electronic components are often formed on a large siliconwafer at the same time. In such a case, the piezoelectric electroniccomponents on the silicon wafer are separated by dicing.

In the piezoelectric electronic component and the process for producingthe same of the present invention, since the thin-film shell member 5can be disposed close to the piezoelectric element 3, it is possible toachieve reductions in size and profile. Furthermore, a conventionalpackage and lid can be omitted, and many steps of die boding, wirebonding, mounting the lid, welding, and the like can also be omitted.Thereby, it is possible to reduce cost.

Furthermore, in the piezoelectric electronic component and the processfor producing the same of the present invention, since the cavity 5 ccan be sealed under a pressure during the film formation, sealing can beeasily performed under vacuum, i.e. under reduced pressure with 10⁻² Paor less. Thus, an expensive special apparatus, such as a welding machinefor welding a lid in vacuum, is unnecessary. In addition, in thepiezoelectric element 3 under reduced pressure, damping due to air canbe reduced, thus improving Q-value.

Furthermore, in the piezoelectric electronic component and the processfor producing the same, as compared with the case of bonding a substratefor sealing, the occurrence of a stress is low, and the piezoelectricelement 3 is difficult to break. In addition, wafer-level packaging canbe performed at a single step, and the exciter 3 d is protected with theshell member 5 in dicing, picking up, and die bonding. Therefore, it ispossible to prevent the breakage of the exciter 3 d.

The material constituting the sacrificial layer 9 preferably has thefollowing properties: (I) the material can be rapidly etched becauseetching is performed through small etching channels, i.e., theconnecting holes 5 b and through holes 5 a (holes through which anetchant for removing the sacrificial layer is introduced); (II) thematerial does not cause damage to the electrodes 3 a and 3 c, a devicematerial such as the piezoelectric thin film 3 b, and the structuralmaterial for the shell member 5; and (III) an etchant for etching thesacrificial layer 9 does not cause damage to the shell member 5, theelectrodes 3 a and 3 c, and the device material, such as thepiezoelectric thin film 3 b.

In the production process according to the first embodiment, thepreferred shape of each of the connecting holes 5 b formed by exposingthe tapers 9 a, which is disposed on the pads 3 a ₁ and 3 c ₁, of thesacrificial layer 9, i.e., the preferred shapes of each of the etchingchannels (holes through which an etchant for removing the sacrificiallayer 9 is introduced), is described below.

In view of sealing the cavity 5 c, the height of the etching channel ispreferably low. When the area of the etching channel is large, an areain which an etchant is brought into contact with the sacrificial layer 9is increased, thus easily etching the sacrificial layer 9. Consequently,in view of the strength retention of the shell member 5, the etchingchannel preferably has a rectangular shape in which the longitudinalside (length in a direction perpendicular to the surface of the siliconsubstrate 1) is short and the transverse side (width in a directionparallel to the surface of the silicon substrate 1) is long.

However, an excessively long transverse side of the etching channelresults in the rise of the middle of the side, thus being difficult toseal the etching channel. Experimental results confirm that when thelong (transverse) side of the etching channel has a length of 30 μm, thesacrificial layer 9 can be sufficiently removed by etching.

The shape of the etching channel is not limited to C, but may be acircle, a square, or another polygon. In particular, in the case of theshape of the etching channel being a circle or a polygon, a stress isdifficult to be concentrated in one direction. Thus, the etching channelis hardly destroyed by a stress.

Second Embodiment

In a second embodiment of a piezoelectric electronic component accordingto the present invention, as shown in FIG. 4, the shell member 5according to the first embodiment has a multilayer structure including,for example, a resin layer 5 e composed of a polyimide serving as theoutermost layer; and an inorganic insulating layer 5 d composed of SiO₂or SiN, the inorganic insulating layer 5 d being disposed at the innerside of the resin layer 5 e. In such a case, moisture resistance andstrength can be imparted by providing a multilayer structure, thusimproving the reliability of the resulting piezoelectric electroniccomponent. In the following embodiments including this embodiment, amember having the same function as that of member in the firstembodiments is represented by the same reference numeral. Redundantdescription is not repeated.

A process for producing the piezoelectric electronic component includesforming an inorganic insulating layer composed of SiO₂ or SiN by thesame method as that for producing the shell member 5 in the firstembodiment; forming a resin layer composed of a polyimide by spincoating; patterning the resin layer by photolithography to form theresin layer 5 e; and performing etching using the resulting resin layer5 e as a mask to form the inorganic insulating layer 5 d. Downstreamsteps are identical to those in the first embodiment.

In the second embodiment, the two-layer structure including thepolyimide resin layer 5 e serving as the outermost layer is exemplified.Various combinations can provide the shell member 5 having variousproperties. For example, the shell member 5 may have three-layerstructure including polyimide/SiO₂/Al₂O₃, the polyimide layer being theoutermost layer.

In the multilayer structure, a combination of an inorganic insulatinglayer having satisfactory moisture resistance, heat resistance, andweather resistance, for example, a SiN layer, a SiO₂ layer, or an Al₂O₃,serving as the lower layer with a resin layer enhancing mechanicalstrength and serving as the upper layer is preferable. In particular,providing at least one SiN layer in the multilayer structure iseffective in improving the moisture resistance and is also effective forthe protection of an Al electrode. The shell member 5 having themultilayer structure includes a high moisture-resistant film serving asthe lowermost layer and a resin provided on the film. Thus, it ispossible to enhance the strength and to improve the moisture resistanceof the shell member 5.

In particular, the shell member 5 may have a multilayer structureincluding a layer having a tensile stress and a layer having acompressive stress. The multilayer structure is preferably designed in amanner such that an absolute value (total stress) of the differencebetween the total of the tensile stress and the total of the compressivestress is smaller than the rupture strength of the shell member 5, andmore preferably the absolute value represents zero.

For example, when a SiO₂ layer having a thickness of 1 μm is formed byRF sputtering, and then a SiN layer having a thickness of 1 μm is formedon the SiO₂ layer by RF sputtering to form the shell member 5 having atwo-layer structure, the SiO₂ layer has a compressive stress of about100 MPa, and the SiN layer has a tensile stress of about 100 MPa.Therefore, the total stress (absolute value of the difference betweenthe total of the tensile stress and the total of the compressive stress)is zero. That is, it is possible to increase the thickness of the shellmember 5 and to improve the strength by the cancellation of thestresses.

In the shell member 5, the SiO₂ layer and SiN layer each having athickness of 1 μm can impart optical transparency to the shell member 5.Thus, the degree of removal of the sacrificial layer 9 by etching can bevisually confirmed, thereby ensuring the removal. Consequently, thereliability of the resulting piezoelectric electronic component can beimproved.

By using the above-described multilayer structure, it is possible tofurther enhance the strength of the shell member 5 and to increase theentire thickness of the shell member 5. Examples of a materialconstituting the layer having a tensile stress include Al₂O₃, SiN, andAlN. Examples of a material constituting the layer having a compressivestress include SiO₂, ZnO, and TaN.

In particular, the use of a SiN film or a SiO₂ film can impart moistureresistance to the shell member 5, can protect an electrode material (inparticular, an Al electrode) and the piezoelectric thin film 3 b, andcan also impart heat resistance to the shell member 5. Furthermore, inparticular, when a resin is used for the shell member 5, it is possibleto impart impact resistance to the shell member 5.

Examples of a material for the resin layer 5 e include an epoxy resin, aresist resin (photosensitive resin) having satisfactory weatherresistance, and a liquid-crystalline polymer having satisfactorymoisture resistance and weather resistance, in addition to a polyimide.In particular, in the case of using the resist resin, the resist resinis patterned and used the resist resin as a mask to directly form theresin layer 5 e. Thereby, the production can be simplified.

A material constituting the resist resin (photosensitive resin)preferably has the following properties: (a) Patterning can be performedby photolithography (ease of patterning); (b) the shrinkage ratio duringcuring is low (protection of the destruction of the shell member 5); (c)Young's modulus is high after curing (sturdy and hard); (d) when heat isapplied, a gas and a low-molecular-weight component are not emitted; (e)electrical characteristics are satisfactory (low dielectric constant,high resistivity); and (f) adhesion to the silicon substrate 1 is high.Specific examples of the material include a “PIMEL” (manufactured byAsahi Kasei Corporation), a “ZFPI”, and a “ZCOAT” (manufactured by ZeonCorporation).

Third Embodiment

A piezoelectric electronic component according to a third embodiment ofthe present invention is suitable for a piezoelectric filter, such as apiezoelectric filter provided on the silicon substrate 1 by combining aplurality of piezoelectric elements 3 into a ladder network as shown inFIG. 5, and a duplexer. As a combination of the plurality of thepiezoelectric element 3, the ladder network is preferable because theinterconnections in which the upper electrode of one piezoelectricelement 3 extending along the surface of the silicon substrate 1functions as the lower electrode of the other piezoelectric element 3can be simplified.

In the third embodiment, as shown in FIGS. 6 and 7, a plurality ofpiezoelectric elements 3 are provided on the silicon substrate 1, andthe shell member 5 covering the piezoelectric elements 3 is formed bythe same production process as that in the first embodiment. FIG. 7 (c)is a schematic view illustrating the structures of the electrodes andthe relationship between the electrodes by virtually removing the shellmember 5 from the piezoelectric electronic component shown in FIG. 7(a).

In this third embodiment, to enhance the strength of the shell member 5,an anchor portion 5 g having a substantially M-shaped cross-section in alongitudinal direction (direction perpendicular to the surface of thesilicon substrate 1) is fixed on the interconnection between theexciters 3 d by bonding. In such a structure, heat is easy to bedissipated with the anchor portion 5 g. As a result, it is possible toimprove power endurance of a piezoelectric filter and duplexer using thepiezoelectric element 3.

With respect to the shape of the end of the sacrificial layer 9 (end ofthe pattern), as shown in FIG. 8 (a), a wedge taper 9 b whose widthgradually decreases toward the end may be used in place of the taper 9a. In this case, the size of the connecting hole 5 b formed from thetaper 9 b can be easily controlled by adjusting the position of thewindows 15 a for etching, thus ensuring the removal of the sacrificiallayer 9 with an etchant 11.

As shown in FIG. 9, in a piezoelectric electronic component according tothis embodiment, electrodes 7 may be bonded to the respective electrodes43 on a mounting substrate 41 with solder balls 35 by ball bonding, andthen these electrodes may be sealed with a sealing resin 37.

In this embodiment, the filter including a plurality of piezoelectricthin-film element combined in a ladder network is exemplified. Thepresent invention is not limited to the example. A filter may becombined to form a lattice network, and a multimode filter may be used.

Fourth Embodiment

In a piezoelectric electronic component according to a fourth embodimentof the present invention, for example, as shown in FIG. 10, anelectrical circuit is provided on the shell member 5. The electricalcircuit includes a resistor, a capacitor, inductor, and the like. Theelectrical circuit may be formed by, for example, forming a metal filmand an insulating film on the upper layer of the shell member 5, andthen patterning these films into a predetermined pattern (for example, ameandering pattern for a resistor).

In this embodiment, as shown in FIGS. 10 (a) and 10 (b), a capacitor canbe formed by forming an insulating layer 51 b composed of SiO₂ or thelike between an electrode layers 51 a and 51 c. Furthermore, as shown inFIG. 10 (c), a spiral conductor 53 is formed on, for example, the anchorportion 5 g on the shell member 5 to form an inductor.

The electrode layer 51 c is connected to the electrode 7 of thepiezoelectric element 3. Therefore, a subsequent connecting step, suchas wire bonding, can be omitted. As a result, the production can besimplified.

Fifth Embodiment

In a piezoelectric electronic component according to a fifth embodimentof the present invention, for example, as shown in FIGS. 11 to 13, asurface acoustic wave filter (hereinafter referred to as a “SAW filter”)60 having an interdigital electrode 63 is used in place of thepiezoelectric element 3. The SAW filter 60 includes an interdigitalelectrode 63 a, reflectors 63 b, the interdigital electrode 63 a beingdisposed between the reflectors 63 b, and pads 63 c and 63 d each beingconnected to the interdigital electrode 63 a, provided on apiezoelectric substrate 61. A member having the same function as that ofmember in the above-described embodiments is represented by the samereference numeral. Redundant description is not repeated.

As shown in FIGS. 12 and 13, the shell member 5 is provided on thepiezoelectric substrate 61 with part of the pad 63 c providedtherebetween and with part of the pad 63 d provided therebetween. As aresult, it is possible to improve impact resistance, to achievereduction in size and profile. In FIG. 13, a sealing resin 65 covers theshell member 5. As a result, in this structure shown in FIG. 13, thesealing resin 65 protects the component, thus improving moistureresistance and impact resistance as compared with those of the structureshown in FIG. 12. The pads 63 c and 63 d are connected to solderportions 7 with connecting electrodes 66.

Each of the piezoelectric electronic components according to theabove-described embodiments can achieve reductions in size and profile,has satisfactory impact resistance, and can improve the yield.Therefore, the piezoelectric electronic components can be suitably usedfor filters, such as duplexers, in communication apparatuses, such ascellular phones.

Japanese Unexamined Patent Application Publication No. 8-162899discloses a SAW filter including a protective member having a hollowstructure, the protective member covering the SAW filter and beingcomposed of a shield metal layer and a resin layer. In this structuredisclosed in Japanese Unexamined Patent Application Publication No.8-162899, to providing a connection to the exterior, there are thefollowing problems.

When the connection to the exterior is made by bump bonding, to form abump on a terminal electrode, the bump must be formed from the openingof the shield metal layer and the resin layer for forming the hollowportion.

However, when the bump is formed from the opening, the bump is broughtinto contact with the shield metal layer to disadvantageously cause ashort. To prevent the contact of the bump to the shield metal layer, itis necessary to increase the opening in size. However, when the openingis increased in size, the strength of the shield metal layer and theresin layer is degraded. As a result, it is difficult to maintain thehollow structure.

Even if wire bonding is employed, it is necessary to prevent the contactbetween wire and the shield metal layer in forming the wire.

Thus, it is also necessary to increase the opening in size. When theopening is increased in size, the strength of the shield metal layer andthe resin layer is degraded. As a result, it is difficult to maintainthe hollow structure.

INDUSTRIAL APPLICABILITY

As has been described above, a piezoelectric electronic component of thepresent invention includes a piezoelectric element on a substrate, padson the piezoelectric element, the pads inputting and outputting theinput and output signals, and a sealing member covering thepiezoelectric element and being remote from the piezoelectric element,wherein the sealing member includes a through hole on each of the pads,the through hole connecting an internal space with an external space,the internal space being ensured by providing the sealing member so thatthe sealing member is remote from the piezoelectric element, and anelectrode is provided so as to occlude the through hole.

In the above structure, by providing the sealing member so that thesealing member is remote from the piezoelectric element in thestructure, it is possible to protect the piezoelectric element withoutinhibiting the oscillations of the piezoelectric element, to provide thesealing member close to the piezoelectric element, and to achievereductions in size and profile.

1. A piezoelectric electronic component comprising: a substrate; apiezoelectric element provided on the substrate, the piezoelectricelement oscillating in response to application of an input signal, andthe piezoelectric element outputting an output signal corresponding tothe oscillation; a plurality of pads provided at the piezoelectricelement; a sealing member comprising an insulating film, the sealingmember covering the piezoelectric element and being remote from thepiezoelectric element, wherein the sealing member includes a throughhole corresponding to each of the pads, the through hole connecting aninternal space with an external space; and an electrode occluding thethrough hole.
 2. The piezoelectric electronic component according toclaim 1, wherein the sealing member comprises at least one compoundselected from the group consisting of a silicon nitride, a siliconoxide, an aluminum oxide, an aluminum nitride, a zinc oxide, a siliconoxynitride, and a tantalum nitride.
 3. A piezoelectric electroniccomponent comprising: a substrate; a piezoelectric element provided onthe substrate, the piezoelectric element oscillating in response toapplication of an input signal, and the piezoelectric element outputtingan output signal corresponding to the oscillation; a plurality of padsprovided at the piezoelectric element; and a sealing member comprisingan insulating film, the sealing member covering the piezoelectricelement and being remote from the piezoelectric element, wherein thesealing member comprises at least one compound selected from the groupconsisting of a silicon nitride, a silicon oxide, an aluminum oxide, analuminum nitride, a zinc oxide, a silicon oxynitride, and a tantalumnitride.
 4. The piezoelectric electronic component according to claim 1,wherein the sealing member has a multilayer structure and includes atleast one film having a compressive stress and at least one film havinga tensile stress.
 5. The piezoelectric electronic component according toclaim 4, wherein the film having a compressive stress comprises at leastone compound selected from the group consisting of SiO2, ZnO, and TaN.6. The piezoelectric electronic component according to claim 4, whereinthe film having a tensile stress comprises at least one compoundselected from the group consisting of Al2O3, SiN, and AlN.
 7. Thepiezoelectric electronic component according to claim 1, wherein thesealing member has a multilayer structure, and the uppermost layercomprises a resin.
 8. The piezoelectric electronic component accordingto claim 7, wherein the resin comprises at least one compound selectedfrom the group consisting of a polyimide, an epoxy resin, a resistresin, and a liquid-crystalline polymer.
 9. The piezoelectric electroniccomponent according to claim 1, further comprising: a connecting holeprovided at the periphery of the sealing member, the connecting holeconnecting the internal space of the sealing member with the externalspace, and an electrode provided so as to occlude the connecting hole,the electrode inputting and outputting the input and output signals. 10.The piezoelectric electronic component according to claim 1, wherein thepiezoelectric element is a piezoelectric resonator including a substratehaving an opening or a depression and an exciter covering the opening orthe depression, the exciter having a structure in which the upper andlower surfaces of a thin film portion including at least onepiezoelectric thin film are sandwiched between at least one pair of anupper electrode and a lower electrode, the upper electrode and lowerelectrode being disposed opposite each other.
 11. The piezoelectricelectronic component according to claim 1, wherein the piezoelectricelement is a piezoelectric filter including a plurality of piezoelectricresonators, each containing a substrate having an opening or adepression and an exciter covering the opening or the depression, theexciter having a structure in which the upper and lower surfaces of athin film portion including at least one piezoelectric thin film aresandwiched between at least one pair of an upper electrode and a lowerelectrode, the upper electrode and lower electrode being disposedopposite each other.
 12. The piezoelectric electronic componentaccording to claim 1, wherein the piezoelectric element is a surfaceacoustic wave device having at least one interdigital electrode on apiezoelectric substrate.
 13. The piezoelectric electronic componentaccording to claim 1, wherein an electrical circuit is provided on thesealing member.
 14. A communication apparatus comprising thepiezoelectric electronic component according to claim
 1. 15. A processfor producing a piezoelectric electronic component such that a sealingmember comprising an insulating film includes a cavity to cover apiezoelectric element on a substrate, the sealing member being remotefrom the piezoelectric element, the process comprising: forming asacrificial layer on the piezoelectric element, the sacrificial layercorresponding to the cavity; forming the sealing member on the entiresurface of the sacrificial layer; partially removing the sealing memberto form an exposed portion partially exposing the sacrificial layer; andremoving the sacrificial layer from the exposed portion.
 16. The processfor producing the piezoelectric electronic component according to claim15, wherein the sacrificial layer is formed into a taper, the height ofthe taper decreasing toward one of the ends of the formed pattern of thesacrificial layer.
 17. The process for producing the piezoelectricelectronic component according to claim 15, wherein the exposed portionis formed at a position facing a pad in the piezoelectric element, thepad being used for inputting and outputting signals.
 18. The process forproducing the piezoelectric electronic component according to claim 15,wherein the sacrificial layer is formed on the piezoelectric element andthe substrate while part of a pad for inputting and outputting signalsremains.
 19. The piezoelectric electronic component according to claim3, wherein the sealing member has a multilayer structure and includes atleast one film having a compressive stress and at least one film havinga tensile stress.
 20. The piezoelectric electronic component accordingto claim 19, wherein the film having a compressive stress comprises atleast one compound selected from the group consisting of SiO2, ZnO, andTaN.
 21. The piezoelectric electronic component according to claim 19,wherein the film having a tensile stress comprises at least one compoundselected from the group consisting of Al2O3, SiN, and AlN.